The long-range goals of this research are to elucidate the rules governing the behavior of tandem duplications and to investigate the mechanism(s) by which tandem duplications arise. The principal goals for the current year were to (1) establish a collection of genetically well defined duplications; (2) to investigate (a) the relationship of left to right ends of duplicated segments, (b) the effect of relaxed packaging restrictions on the distribution of ends, (c) the relationship between genetic length and stability of duplications, and (d) the frequency of non-tandem duplications; (3) to obtain a better estimate of the frequency of duplication foreation; and (4) to establish a reliable genetic map of gene 39. In the coming year our principal objectives will be (1) further analysis of recombination in duplications, (2) the more precise localization of ends within the rII region, (3) investigation of rII regulation by studying the sensitivity to rifampicin of transcription of the r1589 gene in a series of defined duplications and (5) the heteroduplex mapping of duplications and deletions.